Frost, R.L.; Martens, W.N.; Kloprogge, J.T.

Abstract

The use of a Raman microscope combined with a thermal stage enabled the Raman spectra of the three minerals cinnabar, realgar and orpiment. Each of these minerals is of archaeological and medieval interest because of their use as colouring agents. The spectra of these sulphides of Hg and As may be conveniently divided into three sections namely (a) the region centred upon 355 cm-1 where the stretching vibrations are observed (b) the region centred upon 250 cm-1 ascribed to the bending vibrations and (c) the region below 100 cm-1 assigned to the lattice modes. Cinnabar Raman spectra displayed prominent bands 353, 342, 290, 277 and 253cm-1. These bands are assigned to HgS stretching modes and are orientation dependent. The Raman spectrum of realgar shows AsS stretching vibrations at 374, 367, 353, 340 and 327cm-1 and bending modes at 219, 210, 191 and 181cm-1. Orpiment also displays five Raman bands at 382, 355, 325, 310 and 294 cm-1 with bending modes at 202 and 180 cm-1. Differences in the results between this work and published data are accounted for by the sample preparation and the advances in technology with improved signal to noise.